


experimentation

by avosettas



Category: Undertale (Video Game)
Genre: Ecto-Vagina (Undertale), M/M, Scissoring, Sibling Incest, Tribadism, i've never written scissoring before AND IT SHOWS.
Language: English
Status: Completed
Published: 2021-02-19
Updated: 2021-02-19
Packaged: 2021-03-14 17:41:17
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,901
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29545995
Author URL: https://archiveofourown.org/users/avosettas/pseuds/avosettas
Summary: “what’s the point of experimenting if we do the same old thing at the same exact time every time? might as well not experiment at all if you’re gonna make me wait til the usual time.”Or: Sans proposes an experiment. A bedroom-sort of experiment.
Relationships: Papyrus/Sans (Undertale)
Comments: 1
Kudos: 24





	experimentation

**Author's Note:**

> for @robot_kin 
> 
> [head in hands] it's completely hanna's fault that sans keeps saying "kitty".

“hey pap, can we, uh, try something?” When Papyrus looks up from his crossword, Sans is standing in the kitchen entryway. He looks nervous; he won’t meet Papyrus’s eyes, keeping his own trained on the sink. 

“IS IT A SEX THING?” Sans jolts at Papyrus’s responding question, as if he wasn’t expecting an answer. Which is absurd, because Papyrus would _never_ just ignore him! 

But now Sans looks like he wants to disappear into the ground, even though the ground is, of course, covered by their kitchen tiles, and it would certainly take him a long time to dig through them. Especially considering how lazy he is.

Of course, it’s no hassle to explain, not for Papyrus! “I’VE NEVER KNOWN YOU TO HAVE MOTIVATION FOR EXPERIMENTING UNLESS IT WAS FOR SEX, SANS, THAT’S ALL!” 

(Which isn’t… quite true. When they were younger, Sans used to work at the Labs, and though Papyrus doesn’t know _exactly_ what he did there, he knows that it involved science, so it probably involved experiments.) 

(He _does_ remember that when Sans worked in the Labs, he was a lot happier. He had a sense of purpose, and his smiles weren’t so strained.) 

(But! Papyrus _also_ knows that nowadays, he never sees Sans smile quite so widely as when Papyrus kisses him, or when they’re simply sitting on the couch, so close together that it’s hard to tell whose bones are whose.) 

Sans rolls his eyelights a bit. “yeah, yeah, it’s - it’s, uh, a sex thing.” He’s still fidgeting a bit, though Papyrus’s explanation has obviously calmed the worst of his worries. “figured you might be up for a little, uh… fun?” 

“IT’S BARELY ELEVEN IN THE MORNING, THOUGH,” Papyrus argues, because although he _certainly_ isn’t opposed to a bedroom romp, there is a _time_ and a _place_ for it, and as far as he’s concerned, that time is _evening_ and that place is _the bedroom_. 

“what’s the point of experimenting if we do the same old thing at the same exact time every time?” And now Sans is in prime form, coming over to slump on the table across from Papyrus, resting on his elbows. “might as well not experiment at all if you’re gonna make me wait til the usual time.” 

Papyrus sighs, and considers it. That he even _considers_ it - a bedroom romp before evening, how ludicrous - is proof of how far Sans has wormed himself into Papyrus’s soul, as far as he’s concerned. But it _is_ raining today, which means that any activities aside from cleaning, puzzles, and MTTTV marathons are out of the question, and with how dark the sky is, it practically _could_ be evening…

“FINE,” he says, and it’s worth it as soon as he says it, because Sans perks up from his spot across the table. “BUT ONLY! BECAUSE IT’S RAINING, AND I HAVE NO PLANS ANYWAY.”

"cool," Sans replies, visibly relieved, though his tone remains relaxed. "cool, cool, i'll meet you upstairs, yeah?" 

"YES, JUST LET ME CLEAN UP!" Sans is gone in a blink, between one breath and the next. Papyrus doesn't ever bother with manifesting eyelights, but if he did, he'd be rolling them - the stairs are _right_ there! 

Nevertheless, Papyrus folds up the newspaper and sticks it beneath the napkin holder for safekeeping. The pen is dropped in its cup with a clink as he passes the threshold into the living room, though he pauses to stare out at the rain. 

The fat droplets covering the window give the yard a blurred look, an almost dreamlike quality. It's strange, and Papyrus is mostly glad he isn't outside today. Being pelted with cold rain isn't his idea of fun. 

A bedroom romp, however, certainly is! 

He pulls himself from the window and mounts the stairs, taking them two at time easily. When he reaches the landing, his door is still closed, and Sans's is opened a crack. Hopefully he's at least made his bed. Papyrus absolutely, unequivocally refused to partake in any bedroom activities on soiled sheets, especially if they aren't even covering the mattress!

Thankfully, Sans's bed _has_ been made, though it definitely isn't the first thing Papyrus notices when he steps into the room. The first thing he notices is definitely Sans, slumped against the wall with a pillow behind him, with his legs splayed wide open in such a way that Papyrus can see how wet he already is. 

"hey," he says with a crooked grin as Papyrus closes the door. "thought you weren't gonna show up." 

"WELL, IT CERTAINLY LOOKS LIKE YOU GOT STARTED WITHOUT ME," Papyrus retorts. Sans flushes, as if he'd forgotten that his cunt is on display, already leaving a blue-tinted wet spot on the sheets. 

"i got bored." Papyrus snorts as he sits near Sans's feet and begins to loosen his scarf. Already his magic is stirring - because Sans is in such a lewd position, he's sure! In his huff, he almost misses when Sans speaks again. "you're gonna need your kitty, by the way." 

"YOU'RE SO LEWD," Papyrus sighs, though his magic settles into place beneath his clothes. Sans watches disinterestedly as he folds his scarf, and then places his gloves on top of it. The rest of his clothing lands in a heap beside the bed, in a pile that's noticeably more put-together than the trail of clothes Sans has left. 

"alright," Sans says, pushing himself off the mattress with a groan. "pro'bly easier if you sit here…" He maneuvers Papyrus into his vacated spot, straddling his closed legs. It's definitely harder for Papyrus to be embarrassed when he's the one in control, that's for sure!

Sans nudges his legs apart with both hands, before settling himself in the spot they'd been occupying. With a cheeky grin, he lays a hand on the crease between Papyrus's thigh and his cunt, trailing his thumb along the lips. "pretty kitty," he says.

"STOP CALLING IT THAT," Papyrus replies, though his annoyance fades quickly when Sans spreads his folds. His thumb is hardly enough stimulation, but as he continues he licks the index finger on his other hand and presses it to Papyrus's clit, too. 

Papyrus groans, and his head hits the wall with a soft thunk. It's understandable why Sans was slumping, now, although it's not like he couldn't have gotten another pillow. 

That train of thought leaves his head when Sans re-angles the hand spreading him open so that his clitoral hood is pulled back, too. Sans chuckles when he gasps, stroking lightly at his exposed clit with the barest pressure. 

"SANS, I SWEAR," Papyrus growls, though it's probably not all that threatening, all things considered. "IF YOU DON'T _ACTUALLY_ TOUCH ME - HNG!" 

Sans's grin just widens as he continues grinding his palm into Papyrus's clit, the sensation drawing breathy grunts. Papyrus's body slides down the wall slightly as he raises his hips to hump against Sans's palm, pushing himself up by the soles of his feet. 

When his knees start to shake and his grunts to turn soft moans, even despite the exertion, Sans pulls his hand away, smiling sheepishly. Papyrus's body drops back onto the bed, and he glares up at Sans as his cunt twitches from the sudden loss. 

"sorry," Sans says, though he definitely doesn't sound sorry, still staring a Papyrus with shameless hunger. "if it makes y'feel better, i didn't cum before, either." 

"IT DOESN'T MAKE ME FEEL BETTER, NOW PUT YOUR HAND BACK BEFORE I KICK YOU," Papyrus demands. 

"i mean, i _could_ ," Sans replies, emphasizing his answer with a drag of his finger down Papyrus's folds. He continues speaking nonchalantly, completely ignoring the resultant squirming, "but we do have that experiment to try out, remember?" 

"THEN HURRY IT UP," Papyrus says peevishly, "BEFORE I DECIDE TO JUST DO IT MYSELF!"

Sans snorts, but he gets moving, more aware than anyone that Papyrus is a skeleton of his word. Papyrus is abruptly yanked into a proper slumped position, the pillow squished beneath him now. He grumbles as he fixes it, but doesn't push himself back up. Instead, he watches as Sans stares at his pussy like he's trying to remember something. 

"okay, yeah," he mumbles to himself, scooting himself closer. "man, i hate doin' the work." 

Papyrus ignores that, in favor of questioning, "THIS ISN'T SOMETHING YOU SAW IN PORN, IS IT?" 

"i mean, it is," Sans admits, tapping his fingers on Papyrus's tibia. "but it's a thing. did research and everything." 

"WIKIPEDIA DOESN'T COUNT." 

"does cosmo?" Before Papyrus can answer, Sans twists him slightly at the waist, and he yelps. Sans laughs a little, and slots himself between Papyrus's legs, nearly on his back. It's a little awkward - one of his legs and part of his ass are pretty much right on top of Papyrus's thigh, and he's only propped up by his elbows. 

"alright, here we go," Sans says, and then he shifts forward without lifting himself from the bed, rumpling the sheets, unfortunately - that could have been avoided! Papyrus's reprimand dies in his throat, though, because Sans keeps moving until their cunts are touching.

There's a tiny bit of stimulation, but certainly not enough, so Papyrus rolls his hips. Sans fumbles slightly where he'd been grabbing for the other's ankle, falling back onto his elbows. "good?" he asks when he recovers, sounding winded. 

Papyrus shrugs - it wasn't _bad_ , just not enough - as Sans props himself up further, nearly seated correctly on the mattress. "I'M NOT SURE WHAT'S SUPPOSED TO BE HAPPENING HERE," he says as Sans finagles his ankle to nearly rest on his shoulder. 

"that's 'cause i haven't actually started yet," Sans replies deviously. He lays back down, holding Papyrus's ankle against him, and Papyrus watches him over the swell of his own hip with interest. Sans raises his hips experimentally once, then twice. 

Then, he starts humping against Papyrus in earnest, pressing their cunts together messily. _This_ is good, Papyrus decides, rocking his own hips, pointedly ignoring that a mixture of his own slick and Sans's is making its way onto the bed and down his thighs. 

Sans is grunting from exertion, and the entire bed is shaking. He shifts slightly, and suddenly the grinding is pressing him against Papyrus perfectly. Every roll of his hips hits Papyrus's clit, and Papyrus chases after the pleasure, meeting Sans's humping clumsily. Even just hitting against Sans's leg at the pace they've created is good, and soon they're both panting and moaning instead of grunting. 

For once in his life, Papyrus is the first of the two of them cum, arching against Sans. His leg jerks beneath Sans's hold as Sans continues, chasing his own orgasm with a fervor that Papyrus has never quite seen him exert through his lazy exterior. 

Eventually, though, Sans reaches his own end, pressing against Papyrus one last time as he arches against the bed, toes curling into the sheets. It makes Papyrus twitch, though Sans quickly drops away, falling back onto the bed with a slight bounce. 

"ten outta ten," he groans, sleepily raising his hand from Papyrus's leg to give him a thumbs up. 

"YOU HAD BETTER NOT BE FALLING ASLEEP, SANS," Papyrus grumbles, shifting from Sans's hold. He's getting cold, covered in cooling sweat and sitting in a puddle of his and Sans's fluids. 

Sans doesn't respond; he only shoots Papyrus an annoyingly lazy grin without even opening his eye sockets.

**Author's Note:**

> twitter @avosettas


End file.
